1. Field of the Invention
This invention relates to acid resistant glass fibers and a method of forming the same.
2. Description of the Prior Art
Glass fibers are formed by attenuating molten cones of glass from a bushing having a plurality of orifices. The single glass fibers or filaments formed are continuous and generally cylindrical having a diameter of about 1 .times. 10.sup.-5 inches to about 1.0 .times. 10.sup.-3 inches.
After formation, the filaments are sized with an aqueous sizing composition which lubricates the filaments to prevent damage due to abrasion of the filaments against each other during subsequent processing. The sizing composition typically contains a binder which causes the filaments to adhere together when they are formed into strands by gathering in the conventional manner.
These strands can then be formed into yarns, cords or other like materials depending on the final use intended for the glass fibers.
A typical glass fiber composition, hereinafter referred to as "621" glass, being of the "E" glass family, has a typical composition as follows:
______________________________________ Components Percent ______________________________________ SiO.sub.2 53.7 Al.sub.2 O.sub.3 13.4 CaO 21.1 B.sub.2 O.sub.3 8.8 Fe.sub.2 O 0.2 MgO 0.4 TiO.sub.2 0.6 Na.sub.2 O 0.6 F.sub.2 1.4 ______________________________________
The "621" glass composition typified by the above formulation is used to form fibers which have a plurality of uses. The "621" glass composition also has the advantage of having a low melting point and a low liquidus temperature which allows the glass fibers formed therefrom to be melted, refined and to undergo other processing with relative ease in handling.
There are a plurality of known glass fiber compositions; most compositions have a major portion as SiO.sub.2, usually about 50 to 70 percent by weight, however greater or lesser amounts of SiO.sub.2 may be used in the glass fiber compositions for unique applications. The other substances which may be present in the glass composition are Li.sub.2 O, Na.sub.2 O, K.sub.2 O, BeO, MgO, CaO, BaO, TiO.sub.2, ZrO.sub.2, MnO, Fe.sub.2 O.sub.3, NiO, CuO, AgO, ZnO, B.sub.2 O.sub.3, Al.sub.2 O.sub.3, F.sub.2, WO.sub.3, CeO.sub.2, SnO.sub.2, and the like. The selection of a particular glass composition is made in accordance with the desired processing characteristics and the final properties of the glass fibers desired for a particular use.
Glass fibers in the form of cloth have found particular utility as filter bags to be used for filtering high temperature gases from industrial stacks. These gases contain many corrosive materials. For example, a stack gas produced from a coking process contains water vapor and SO.sub.3 which forms sulfuric acid. The sulfuric acid attacks the surface of the glass fibers causing reduced filter bag life, hence, necessitating replacement of the filter bags at very short intervals. Thus, it is desired that acid resistant glass fibers be economically produced so that thay may be utilized in the filtration of corrosive liquids and gases.
An additional use of glass fibers is for the reinforcement of resinous materials. Typically, glass fibers in the form of cloth, mat, strand, or yarn are impregnated with a resinous solution which is hardened to form a generally rigid article. The glass fibers provide strength to the article because their tensile strength is substantially greater than the plastic material forming the resin matrix. These fiber reinforced plastics have found utility when fabricated as storage tanks for a plurality of materials. In some instances, the materials to be stored are corrosive in nature, having a highly acidic character, and therefore have a tendency to attack the glass fibers, thereby reducing the life of the storage tanks. Therefore, it has been desired to have glass fibers which are resistant to attack by acidic media for glass fiber reinforced storage tanks.
In accordance with the instant invention, an acid resistant glass fiber and a process for producing an acid resistant glass fiber is provided.